The overall objectives of this research are to (1) investigate the biology of the Mycoplasmatales with particular reference to their arthritogenic properties and (2) to relate the mechanisms of pathogenesis of chronic mouse arthritis with the possible etiology of human rheumatoid arthritis. Mycoplasma arthritidis and M. pulmonis-induced arthritides of mice will be used as models of chronic inflammation. The mechanisms of pathogenesis will be investigated in regards to (1) persistence of antigens, (2) biological mimicry resulting in development of autoimmunity, (3) mycoplasma induced antigenic alteration of host tissues, (4) immune complex disease, and (5) delayed hypersensitivity phenomena. Emphasis will also be placed upon mycoplasma/host cell interactions and resulting induction of interferon. Using cultural and serological methods, attempts will be made to detect evidence of mycoplasmal infection in patients exhibiting rheumatoid arthritis.